1. Field of the Invention
This invention relates to heat pump type air conditioning apparatus having a variable capacity compressor, and more particulaly to such an apparatus having a control device for preventing compressor lock upon restart after completing a defrosting cycle.
2. Description of the Prior Art
Conventionally, after prolonged heating cycle usage, the efficiency of the heat pump type air conditioning apparatus is lowered due to the outdoor heat exchanger becoming coated with frost or ice. Then, in order to defrost the accumulated frost or ice, the apparatus changes from a heating cycle to a cooling cycle. During such defrosting, the low temperature refrigerant flows into the indoor heat exchanger and the room temperature decreases. As a result, it is necessary to shorten the defrosting time in order to decrease the resulting room temperature drop.
In order to shorten the defrosting time, it is necessary to operate the compressor at high capacity during defrosting. However, this approach has the following problems.
At the end of the defrosting time, the refrigerant in the outdoor heat exchanger is in a liquid state under high pressure. Therefore when the heating cycle resumes operation after defrosting, the liquid refrigerant in the outdoor heat exchanger flows into the compressor and the refrigerant in the compressor dissolves into the lubricant which is used to lubricate the moving or rotating parts of the compressor. As a result, the lubricating performance of the lubricant decreases.
Moreover, the compressor must be operated at high capacity because the room temperature is low when the heating cycle restarts. When the compressor is operated at high revolutions under such conditions, the compressor cannot operate smoothly and in an extreme case the compressor locks and cease operation altogether.